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Published in IET Microwaves, Antennas & Propagation
Received on 22nd February 2011
Revised on 14th May 2011
doi: 10.1049/iet-map.2011.0099
ISSN 1751-8725
Dual-band matching technique based on
dual-characteristic impedance transformers
for dual-band power amplifiers design
K. Rawat F.M. Ghannouchi
iRadio Laboratory, Department of Electrical and Computer Engineering, Schulich School of Engineering,
University of Calgary, Calgary AB, Canada T2N 1N4
E-mail: krawat@ucalgary.ca
Abstract: This study demonstrates a novel matching network synthesis technique that matches any arbitrary reflection coefficient
seen by the active device at two uncorrelated frequencies to the standard 50 V load. The proposed matching network is fully
transmission line based and, hence, can be used in high-power applications at higher frequencies. Unlike previously reported
dual-band matching techniques, this work proposes and discusses various ways to achieve realisable solutions for arbitrary
frequency ratios that account for fabrication limitations. The proposed synthesis approach is validated with the design and
fabrication of a 10 W gallium nitride (GaN)-based class-AB amplifier for code division multiple access and Worldwide
Interoperability for Microwave Access applications at 1960 and 3500 MHz. The amplifier has 59.8 and 55.1% drain
efficiencies at saturation in the first and second bands, respectively.
1 Introduction
The introduction of modern communication standards has
motivated the design of a dual-band power amplifier (PA),
especially in concern with base station transmitters. The use
of a dual-band PA provides savings, in terms of hardware
as well as re-configurability, for their use in software-
defined radio architectures [1]. This also motivates wireless
communication network industries to develop dual-band
base stations and repeaters [2]. Moreover, a wide-band
option is difficult to apply in the case of PA design for
maintaining optimum efficiencies over the band, especially,
when the bandwidth is intend to cover the two
communication standards far apart in terms of their carrier
frequencies. For such cases, dual-band matching provides
an optimum solution over a limited range of bandwidth
around the two carrier frequencies of operation.
In the past, several attempts have been made to design such
dual-band PAs and their corresponding dual-band matching
circuits [3–15]. Among these, some of the attempts are
based on lumped components [3– 5], but they are limited
by high power handling and the low Q factor performance
of the lumped components, especially for high radio
frequency (RF) frequencies. Some designs, however, utilise
transmission line-based impedance transformers [6–8], but
they are suitable only for real impedance matching, which
is not always the case while designing a matching circuit
for an RF PA.
Moreover, an interesting effort has been reported for
matching harmonics using the transmission line-based
matching technique [9, 10]. Such a matching network is
quite good for matching high-reactive impedances, which
are usually required in harmonic terminations; however, it
cannot be used as such for fundamental complex matching
with high-resistive components at two separate and
uncorrelated frequencies simultaneously. Consequently, for
the common practice of using load-pull data, which needs
matching for complex loads with real parts, this approach
falls short of expectations.
It is also worth mentioning that, for dual-band PA design,
the required complex loads seen by the device at two bands of
operations can be different and can have any arbitrary values.
This hinders the use of some previous works reported in this
field [11, 12], as they limit the performance of the PA design.
Recently, some new matching techniques have considered
the necessity for matching two different complex loads to
50 V at two frequencies [13–15], but the methodology and
the design equations are too complex and need a higher
order of numerical optimisations that find their convergence
for only selected frequency ratios and complex input
impedances. Moreover, some of these techniques also report
results using very high characteristic impedances of
transmission lines, which correspond to narrow lines that
are difficult to fabricate with the standard fabrication
process [11, 14, 15].
In the light of these issues, this paper presents a new
dual-band matching technique, which utilises the dual-band/
dual-characteristic impedance transformer approach. The
proposed design methodology calls for the use of a novel
dual-band impedance transformer, which has different
characteristic impedances at two frequencies of operation.
This transformer utilises dual-band conventional T-type and
1720 IET Microw. Antennas Propag., 2011, Vol. 5, Iss. 14, pp. 1720–1729
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The Institution of Engineering and Technology 2011 doi: 10.1049/iet-map.2011.0099
www.ietdl.org